The Ubiquitous Sensor Network (USN) is one of the core techniques of ubiquitous computing technology and is technology in which data generated by combining a variety of sensor nodes is associated with an application server. Unlike common sensors, but like intelligent computers, the sensors have the ability to collect or process various cases of generated data.
Monitoring using a single sensor is limited in terms of a monitoring area or accuracy according to the level of hardware. If pieces of information collected by several nodes are merged, however, the information can be monitored more accurately and reliably than the situations of the real world.
Fields to which the USN may be applied include monitoring fields for a variety of phenomena in the real world, such as disaster prevention, environment monitoring, intelligent physical distribution management, real-time monitoring, mobile healthcare, home security, and machine diagnosis and may also include a lot of application fields requiring remote monitoring.
In the USN, a lot of nodes are distributed in order perform monitoring tasks over a wide area, data sensed by sensors is changed to upper events through data processing within the network and then transferred to a remote administrator. Here, data is transmitted through a multi-hop wireless network of a low speed and low power.
Meanwhile, in Korea, the USN (that is, the next-generation network), together with IPv6 and BcN, has been selected as one of the three infra technologies of IT 839, and all its strength is being concentrated on the development of the technology.
Such wireless communication network techniques include techniques, such as Bluetooth, ZigBee, and Motes. The techniques, however, are impossible to use for u-City Core service because they have various problems, such as an excessively long association time, insufficient extensibility to the mesh network, non-mobility support for devices, great power consumption, and difficulty in extending addressing. In order to solve the problems, a Wireless Beacon-enabled Energy-Efficient Mesh network (WiBEEM) technology has been developed.
In the newly developed WiBEEM technology, all networks are synchronized as one network using a beacon and are configured to support a mesh network operation with low power on the basis of a beacon collision avoidance technique. Furthermore, since short addresses can be efficiently allocated using a Next Address Available (NAA)-based address allocation method, a maximum of 65,536 devices can be controlled. Accordingly, the WiBEEM technology can be used not only within a home, but also in the u-City.
The most significant characteristic of the WiBEEM technology lies in that the WiBEEM technology is an efficient wireless network in which a mesh network is stably operated even in the beacon mode, thus consuming low power. The fact that the wireless mesh network is stably operated corresponds to technology which is one step higher than the existing wireless communication technology using wired communication technology as a backbone network, and it is meant that not only all sensor network nodes within a communication range, but also nodes outside the RF range can communicate with each other through intermediate nodes if the intermediate nodes exist.
The above WiBEEM technology is a wireless protocol which provides an efficient communication method for WPAN applications and supports mobility according to ubiquitous environments.
An advantage when the mesh network is operated in the beacon mode, as in the WiBEEM protocol, is that the efficiency of power consumption can be improved because each node can determine the time of an inactive period in which the node can enter a period where it is operated in a deep sleep mode period DSP.
The WiBEEM protocol also has a significant advantage in that it supports mobility. If mobility is supported, autonomy in the communication area where free communication is possible anywhere within the WPAN can be achieved.
The conventional WiBEEM standard, however, is not USN technology supporting stable QoS. For example, in the case where an old person pays a higher service charge than other people and asks for his stable health, a system capable of providing different kinds of services from only very basic services required for healthy young men with a small amount of money and QoS according to the different kinds of services has to be provided to the old person. Accordingly, in the WiBEEM technology, QoS support technology has a very important meaning.
Furthermore, in the case of underground utility management, sensor information for the leakage detection of city gas requires a different level of QoS from sensor information for water service management. Accordingly, a method of differently arranging QoS parameters according to different services and setting a different backoff time in a Contention Access Period (CAP) period needs to be used.